1. Field of the Invention
The present invention relates generally to a non-aqueous electrolyte battery including a positive electrode which uses, as a positive electrode material, a lithium-metal compound oxide containing Co, Ni, Mn and the like besides Li, a negative electrode, and a non-aqueous electrolyte solution as well as to a positive electrode material for use in such a non-aqueous electrolyte battery and a process for preparing the same.
2. Description of the Related Art
Recently, non-aqueous electrolyte batteries of high electromotive force have come into practical use, as one type of advanced batteries featuring high power and high energy density. The non-aqueous electrolyte battery uses a non-aqueous electrolyte solution as the electrolyte, taking advantage of oxidation and reduction of lithium.
Such a non-aqueous electrolyte battery has generally employed, as the positive electrode material, a lithium-metal compound oxide containing Co, Ni, Mn and the like so as to obtain high voltage.
Where such a lithium-metal compound oxide is used as the positive electrode material, however, the positive electrode material reacts with the non-aqueous electrolyte solution to decompose the non-aqueous electrolyte solution and hence, lowered preservability and charge-discharge cycle characteristics of the battery result.
More recently, there has been designed a non-aqueous electrolyte battery wherein a mixture solvent of propylene carbonate and diethyl carbonate is used as a solvent in the non-aqueous electrolyte solution thereby inhibiting the aforesaid reaction of a compound oxide of lithium and transition metal s with the non-aqueous electrolyte solution, as disclosed in Japanese Unexamined Patent Publication No.4(1992)-184872.
However, in the case where the compound oxide of lithium and metals including Co, Ni, Mn and the like is used as the positive electrode material, particularly when the battery is in a charged state, there still occurs this reaction of the positive electrode material with the non-aqueous electrolyte solution and hence, a lowered charge preservability of the battery results.
Where LiCoO.sub.2 or LiNiO.sub.2 is used as the positive electrode material, a high discharge voltage of about 4 V is obtained for an increased energy density of the battery. Accordingly, studies have recently been made on the use of such lithium-metal compound oxides.
Unfortunately, however, the aforesaid lithium-metal compound oxides do not have a stable crystalline structure and therefore, repeated charging and discharging of the non-aqueous electrolyte battery results in destruction of the crystalline structure of the lithium-metal compound oxide. Thus, the non-aqueous electrolyte battery is gradually decreased in the discharge capacity, failing to offer a satisfactory charge-discharge cycle characteristics.
More recently, there has been proposed by Japanese Unexamined Patent Publication No.6(1994)-267539, the use of a lithium-nickel compound oxide as the positive electrode material, which compound oxide has a full width at half maximum of a peak indicative of (003) Plane in a range of between 0.14.degree. and 0.30.degree., as measured by the powder X-ray diffraction analysis using a Cu-K.alpha. X-ray source. Further, there has been proposed by Japanese Unexamined Patent Publication No.8(1996)-222223, the use of a compound oxide of lithium, cobalt and a transition metal other than cobalt, as the positive electrode material, which compound oxide has full widths at half maximum indicative of (003) Plane and (104) Plane in a range of not greater than 0.5.degree., as measured by the X-ray diffraction analysis.
Where, as suggested by Japanese Unexamined Patent Publication No.6(1994)-267539, the lithium-nickel compound oxide with its crystallinity controlled in the aforementioned manner is used as the positive electrode material, the charge-discharge cycle characteristics and discharge capacity of the non-aqueous electrolyte battery are improved to a degree as compared with a case where the crystallinity of the compound oxide is not controlled. Unfortunately, however, even the non-aqueous electrolyte battery using such a positive electrode material still suffers the destruction of the crystalline structure of the material due to the repeated charging and discharging of the battery. As a result, the non-aqueous electrolyte battery has not accomplished a sufficient improvement in the charge-discharge cycle characteristics.
In the case where used as the positive electrode material is the compound oxide containing lithium, cobalt and a transition metal other than cobalt, such as nickel, manganese and the like, and where the crystallinity of the compound oxide is controlled in the aforementioned manner, as disclosed in Japanese Unexamined Patent Publication No.8(1996)-222223, the compound oxide does not have a sufficiently stable crystalline structure and therefore, repeated charging and discharging of the battery involves change in the crystalline structure. Consequently, the non-aqueous electrolyte battery cannot accomplish a sufficient improvement in the charge-discharge cycle characteristics.